1. Field of the Invention
This invention relates to suspension systems for automotive vehicles and machines which receive mechanical shock, and more particularly to a piston post for a damper.
2. Description of Related Art
Dampers are used in connection with automotive suspension systems to absorb unwanted vibrations which occur during driving. To dampen unwanted vibrations, dampers are generally connected between the body and the suspension of the automotive vehicle. A piston assembly is located within the damper and is connected to the body of the automotive vehicle through a piston post which in turn is connected to a piston rod. Because the piston assembly is able to limit the flow of damping fluid within the working chamber of the damper when the damper is compressed or extended, the damper is able to provide a damping force which "smooths" or "dampens" vibrations transmitted from the suspension to the body.
The greater the degree to which the flow of damping fluid within the working chamber is restricted by the piston assembly, the greater the damping forces which are provided by the damper. Accordingly, a "soft" compression and rebound stroke is produced when the flow of damping fluid in the working chamber is relatively unrestricted. In contrast, a "firm" compression and rebound stroke is produced when there is an increased restriction in the flow of damping fluid in the working chamber.
Because different driving characteristics depend on the amount of damping forces the damper provides, it is often desirable to have a damper in which the amount of damping forces generated by the damper is adjustable. One method for selectively changing the damping characteristics of a damper is disclosed in U.S. Pat. No. 4,890,858. This reference discloses a damping system in which a switch is used to control the damping characteristics of a suspension system. In this regard, the switch is used to control the position of a rotary valve inside each of the dampers in the suspension system. The rotary valve is in turn used to control the flow of damping fluid between the upper and lower portions of the working chamber so as to change damping characteristics.
While such dampers are effective in providing adjustable damping forces, they are sometimes susceptible to certain improvements. For example, the piston post is sometimes relatively long so as to accommodate the various components of the piston such as an annular spacer which is used to bias the valve disk associated with the piston. This is undesirable because the piston post adds to "dead length" of the damper since it remains within the pressure cylinder during operation of the damper. In addition, the piston rod sometimes has holes in its lower portion which are used to establish bypass passages around the piston. The formation of these bypass passages generally require several additional manufacturing operations which increase the cost of producing the piston rod. Further, the wall thickness of the piston rod has to be larger than is otherwise desired to accommodate the presence of the holes while still maintaining the desired strength of the piston rod.